The Transportation Security Administration (TSA) and international regulators seek security measures to help reduce the likelihood of a direct replication of 9/11, in which commercial passenger airliners were commandeered by small bands of terrorists, kept under control for some time, and then crashed into specific targets. This paper compares, for the U.S. case, the costs and benefits of three specific security measures designed for that purpose, assessing risk reduction, losses, and security costs in the context of the full set of security layers. These three measures are Installed Physical Secondary Barriers (IPSB) to restrict access to the hardened cockpit door during door transitions, the Federal Air Marshal Service (FAMS), and the Federal Flight Deck Officer (FFDO) program. Since the FAMS costs $1.2 billion per year, and its effectiveness is in serious doubt, a alternate policy measure considered is to double the budget of the FFDO program to $44 million per year, install IPSBs in all U.S. aircraft at a cost of $13.5 million per year, and reduce funding for FAMS by 75% to $300 million per year. A break-even cost-benefit analysis then finds the minimum probability of an otherwise successful attack required for the benefit of security measures to equal their cost. It was found that the IPSB is cost-effective if the annual attack probability exceeds 0.5% or 1 attack every 200 years. The FFDO program is cost-effective if the annual attack probability exceeds 2.8%. On the other hand, more than four attacks per year need to be deterred, foiled, prevented or disrupted for FAMS to be cost-effective. Thus, even when assumptions are in place that considerably bias the analysis toward the opposite conclusion, the expensive FAMS very substantially fails a cost-benefit assessment. Moreover, insofar as FAMS does reduce risk, almost all of that benefit can be obtained with a mix of inexpensive measures: IPSB and FFDOs. A policy that includes IPSBs, an increased budget for FFDOs, and a reduced budget for FAMS may well be optimal.

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Centre for Infrastructure Performance and Reliability Research Report 281.12.2011